The present invention relates to a self-powered gamma detector which can hold the influence of neutron rays to the minimum, and can measure the dose of gamma rays accurately under a high neutron environment in the reactor etc. Here, “self-powered detector” means that neither an internal power supply nor an external power supply are needed, and the detector itself can give the power output due to the incidence of gamma rays to the detector.
As a self-powered in-core gamma detector (hereafter, referred to as SPGD) which is used in a nuclear reactor, a γ thermometer has been developed to date. In the γ thermometer, the temperature of the iron etc. installed in a small vacuum-insulated space is raised by the γ heat generation. It is, therefore, possible to obtain the strength of the gamma ray by measuring the temperature rise by using a thermocouple. For instance, a reactor power monitoring system comprising a local monitoring system using a self-powered detector and a gamma thermometer for calibration is disclosed in JP 2007-285990 A. The monitoring system disclosed here is used to observe the reactor power overall. The gamma thermometer for calibration is composed so as to measure the heat generation temperature by a differential thermocouple by using the heat generation phenomenon in the stainless steel caused by gamma rays, and to measure the gamma ray output distribution.
Moreover, there is a neutron detector described in JP 2006-0208160 A as the in-core detector which has a similar structure to the present invention though it is the detector not for gamma rays but neutron rays. In this neutron detector, electrons generated due to the nuclear reaction caused when a thermal neutron ray is incident on the emitter member move from a columnar emitter to a collector, the electric current caused by the movement of the electrons is measured by an ammeter through a MI (Mineral Insulated) cable, and thermal neutron flux is measured from the current value obtained.